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비선형 k-ε 모형을 이용한 부분 식생 개수로 흐름의 평균흐름 및 난류구조 수치모의
최성욱,최성욱,김태준,Choi, Seongwook,Choi, Sung-Uk,Kim, Taejoon 대한토목학회 2014 대한토목학회논문집 Vol.34 No.3
본 연구에서는 부분 식생된 개수로에서 평균흐름 및 난류구조에 관한 수치모의 결과를 제시하였다. 이를 위하여 식생항력항이 포함된 레이놀즈 평균 Navier-Stokes 방정식을 수치해석 하였고 난류 모형으로 비선형 k-${\varepsilon}$ 모형을 이용하였다. 제시된 모형을 Nezu and Onitsuka (2001)의 실험수로에 적용하여 모의된 결과를 실험 계측자료 및 Kang and Choi (2006)의 Reynolds stress model 모의결과와 비교하였다. 실험결과와 비교한 결과에 따르면, 비선형 k-${\varepsilon}$ 모형이 평균흐름의 대체적인 경향을 잘 모의하는 것으로 확인되었다. 또한, 식생 영역과 비식생 영역의 경계면에서 쌍와 (twin vortices)가 생성되고 난류강도와 레이놀즈 응력의 최대점이 위치하는 것을 확인하였다. 레이놀즈 응력에 대해서는 경향은 잘 모의하지만 정량적으로 과소 산정하는 것으로 나타났다. This study presents a numerical modeling of mean flow and turbulence structures of partly-vegetated open-channel flows. For this, Reynolds-averaged Navier-Stokes equations with vegetation drag terms are solved numerically using the non-linear k-${\varepsilon}$ model. The numerical model is applied to laboratory experiments of Nezu and Onitsuka (2001), and simulated results are compared with data from measurement and computations by Kang and Choi's (2006) Reynolds stress model. The simulation results indicate that the proposed numerical model simulates the mean flow well. Twin vortices are found to be generated at the interface between vegetated and non-vegetated zones, where turbulence intensity and Reynolds stress show their maximums. The model simulates the pattern of the Reynolds stress well but under-predicts the intensity of Reynolds stress slightly.
A Pseudobipolar Junction Transistor for a Sensitive Optical Detection of Biomolecules
Seongwook Choi,Joongsoo Moon,Sangwoo Lee,Yongjun Hwang,Young June Park IEEE 2016 IEEE transactions on electron devices Vol.63 No.5
<P>A new optical sensor system, called the pseudo-bipolar junction transistor (BJT) optical measurement system (PBOS), based on a pseudo-BVceo of the BJT is proposed by adding a back-to-back connection of a laser diode (LD) (or an LED) and a p-i-n photodiode (PD) in the conventional optical measurement system operated in the photoconductive mode. A back-to-back connection of two optoelectronic devices and illumination of the light from the LD to the PD generates an optical current gain in the PD. It is similar to the current flowing mechanism in the BJT under the base open condition, in which the forward emitter-base junction current generates an electrical current gain in the base-collector junction. Similar to the negative differential resistance (NDR) after BVceo of the BJT, the NDR is observed in the PBOS. Operating the PBOS in the NDR region, the system can provide much higher sensitivity and lower limit of detection compared with the conventional optical measurement system in the photoconductive mode with a p-i-n PD. We show a mathematical model of the sensitivity of the PBOS to the transmittance of the optical path and our initial data for glucose detection as a potential application of the system.</P>
Numerical simulation of dense interflow using the k-ε turbulence model
Choi, Seongwook,Choi, Sung-Uk 한국수자원학회 2017 한국수자원학회논문집 Vol.50 No.9
본 연구에서는 중층 밀도류를 모의할 수 있는 k-ε 난류모형의 지배방정식을 제시하고 수치모의를 수행하였다. 깊은 수체에 모형을 적용하여 중층 밀도류를 모의하고 게산된 유속과 초과밀도 분포를 분석하였다. 밀도류의 주 흐름방향을 따라 물 연행으로 인해 유속이 감소되는 것과 Richardson 수의 증가로 인해 유속 변화율이 감소되는 것을 관찰하였다. 유속과 초과밀도의 유사성을 확인하였으나, 난류운동에너지와 소산율의 유사성에서는 보이지 않았다. k-ε 모형의 모의 결과를 이용하여 중층 밀도류의 층적분 모형에서 사용될 수 있는 형상계수를 계산하였다. 또한, 층적분 모형을 이용하여 k-ε 모형에서 사용되는 부력관련 모형상수 (c₃ɛ)와 부피팽창계수 (β0)를 계산하였다. This study presents a numerical model for simulating dense interflows. The governing equations are provided and the finite difference method is used with the k-ε turbulence model. The model is used to simulate a dense interflow established in a deep ambient water, resulting velocity and excess density profiles. It is observed that velocity decreases in the longitudinal direction due to water entrainment in the vicinity of the outlet and rarely changes for increased Richardson number. Similarity collapses of velocity and excess density are obtained, but those of turbulent kinetic energy and dissipation rate are not. A shape factor for the dense interflow is obtained from the simulated profiles. The value of this shape factor can be used in the layer-averaged modeling of dense interflows. In addition, a buoyancy-related parameter (c₃ɛ) for the k-ε model and the volume expansion coefficient (β0) are obtained from the simulated results.
Choi, Ki Hong,Han, Seongwook,Lee, Ga Yeon,Choi, Jin-Oh,Jeon, Eun-Seok,Lee, Hae-Young,Lee, Sang Eun,Kim, Jae-Joong,Chae, Shung Chull,Baek, Sang Hong,Kang, Seok-Min,Choi, Dong-Ju,Yoo, Byung-Su,Kim, Kye The Korean Society of Cardiology 2018 Korean Circulation Journal Vol.48 No.11
<P><B>Background and Objectives</B></P><P>The prognostic impact of left axis deviation (LAD) on clinical outcomes in acute heart failure syndrome (AHFS) with left bundle branch block (LBBB) is unknown. The aim of this study was to determine the prognostic significance of axis deviation in acute heart failure patients with LBBB.</P><P><B>Methods</B></P><P>Between March 2011 and February 2014, 292 consecutive AHFS patients with LBBB were recruited from 10 tertiary university hospitals. They were divided into groups with no LAD (n=189) or with LAD (n=103) groups according to QRS axis <−30 degree. The primary outcome was all-cause mortality.</P><P><B>Results</B></P><P>The median follow-up duration was 24 months. On multivariate analysis, the rate of all-cause death did not significantly differ between the normal axis and LAD groups (39.7% vs. 46.6%, adjusted hazard ratio, 1.01; 95% confidence interval, 0.66, 1.53; p=0.97). However, on the multiple linear regression analysis to evaluate the predictors of the left ventricular ejection fraction (LVEF), presence of LAD significantly predicted a worse LVEF (adjusted beta, −3.25; 95% confidence interval, −5.82, −0.67; p=0.01). Right ventricle (RV) dilatation was defined as at least 2 of 3 electrocardiographic criteria (late R in lead aVR, low voltages in limb leads, and R/S ratio <1 in lead V<SUB>5</SUB>) and was more frequent in the LAD group than in the normal axis group (p<0.001).</P><P><B>Conclusions</B></P><P>Among the AHFS with LBBB patients, LAD did not predict mortality, but it could be used as a significant predictor of worse LVEF and RV dilatation (Trial registry at KorAHF registry, ClinicalTrial.gov, NCT01389843).</P>
최성욱(Choi Sung-Uk),최성욱(Choi Seongwook) 대한토목학회 2012 대한토목학회논문집 B Vol.32 No.1B
This study presents a numerical model that is capable of simulating the evolution of mining pit in a stream. The numerical model is based on the quasi-steady assumption that the flow is steady with time-dependent morphological change. This hypothesis is valid due to the fact that the stream morphology changes over a long period compared with the time of flow change. Before applications, numerical experiments are carried out with two total load formulas such as Engelund and Hansen's (1967) and Ackers and White's (1973). It is found that the use of Engelund and Hansen's formula reproduces evolution of mining pit best compared with simulated profiles in Parker (2004). Then, the model is applied to two laboratory experiments in the literature. In general, the numerical model simulates properly the evolution of mining pit in laboratory open-channels. However, it is found that the model does not reproduce head-cutting, propagating upstream, and under-estimates the wave of the bed, propagating downstream, after finishing the re-fill of the mining pit. 본 연구에서는 하천에서 준설 웅덩이의 발달과정을 모의할 수 있는 수치모형을 제시하였다. 제시된 수치모형은 준정류 가정에 기초하는데, 이는 흐름은 정상류이고 하상은 시간에 따라 변한다고 가정하는 것이다. 준정류 모형은 흐름에 비해 하도변형이 장기간에 걸쳐 진행된다는 사실에 근거한다. 총유사량 공식으로 Engelund and Hansen 공식과 Ackers and White 공식을 이용하여 수치실험을 실시하였다. Engelund and Hansen 공식을 사용하였을 때, Parker(2004)에 제시된 준설웅덩이의 되메움 과정을 정량적으로 유사하게 모의하는 것으로 나타났다. 제시된 모형의 적용성을 검토하기 위하여 선행 실내실험에 적용하였다. 전반적으로 준정류 모형이 실험수로에서 웅덩이의 발달과정을 잘 모의하는 것으로 확인되었다. 그러나 수치모형이 웅덩이 상류측으로 전파되는 두부침식 현상을 재현하지 못하며, 되메움 이후 하류로 전파되는 하상파를 과소 산정하는 것으로 나타났다.